mm: move responsibility for setting SWP_FS_OPS to ->swap_activate

If a filesystem wishes to handle all swap IO itself (via ->direct_IO and
->readpage), rather than just providing devices addresses for
submit_bio(), SWP_FS_OPS must be set.

Currently the protocol for setting this it to have ->swap_activate return
zero.  In that case SWP_FS_OPS is set, and add_swap_extent() is called for
the entire file.

This is a little clumsy as different return values for ->swap_activate
have quite different meanings, and it makes it hard to search for which
filesystems require SWP_FS_OPS to be set.

So remove the special meaning of a zero return, and require the filesystem
to set SWP_FS_OPS if it so desires, and to always call add_swap_extent()
as required.

Currently only NFS and CIFS return zero for add_swap_extent().

Link: https://lkml.kernel.org/r/164859778123.29473.17908205846599043598.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 3 insertions, 7 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index f08bf675a613..d811458c0a88 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2259,13 +2259,9 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 
 	if (mapping->a_ops->swap_activate) {
 		ret = mapping->a_ops->swap_activate(sis, swap_file, span);
-		if (ret >= 0)
-			sis->flags |= SWP_ACTIVATED;
-		if (!ret) {
-			sis->flags |= SWP_FS_OPS;
-			ret = add_swap_extent(sis, 0, sis->max, 0);
-			*span = sis->pages;
-		}
+		if (ret < 0)
+			return ret;
+		sis->flags |= SWP_ACTIVATED;
 		return ret;
 	}